Method and apparatus for air cooling glass tube

ABSTRACT

HIGH VELOCITY AIR IS SUPPLIED TO A CONFINED SPACE ALONG AN EXTENDED LENGTH OF NEWLY FORMED GLASS ROD OR TUBING TO PROVIDE IMPROVED COMTROLLED COOLING RATE AND THEREBY PERMIT HIGHER PRODUCTION RATES, AND IMPROVED THERMAL STRESS CONTROL.

' Jan. 1971 R. w. WILSON 3,554,723 U METHOD AND APPARATUS FOR AIRcooLImGLAss TUBE Filed Aug. 1967 V l' I I. l f\ I I 3 Q co Q gq t l I,3'\ Q x J\ i O\ I n A INVENTOR.

RICHMOND w. WILSON BY M WJZJLM ATTORNEY States PatentfO METHOD ANDAPPARATUS FOR AIR. COOLING GLASS TUBE Richmond W. Wilson, Corning, N.Y.,assignor to Corning Glass Works, Corning, N.Y., a corporation of NewYork Filed Aug. 4, 1967, Ser. No. 658,572

lntLCl. C03b /14 us. (:1. 65-86 6 Claims ABSTRACT OF THE DISCLOSURE Highvelocity air is supplied to a confined space along an extended length ofnewly formed glass rod or tubing to provide improved controlled coolingrates and thereby permit higher production rates, and improved thermalstress control.

BACKGROUND OF THE INVENTION In form-ing glass tubing by either an updrawor downdraw process, including both hollow and solid tubing, acontinuous length of such tubing is drawn from a suitable orifice andusually pulled horizontally along a plurality of support rollers ordiabolos. However, due to its high heat of formation, extremely longcooling lines have been required in order to sufiilciently reduce thetemperature of the tubing to a temperature where it could be cut withoutimparting deformation. Production speeds for drawing tubing have,therefore, been limited by the space available for the cooling lines,since the tubing must be cooled to a predetermined temperature before itcan be cut to size.

United States Pat. No. 3,260,586 to Prohaszka et al. indicates thatforced air cooling of hollow tubing has been tried in the past, but wasfound to be quite slow. In addition, the patent states that watercooling, although much faster, normally introduces uneven coolingeffects. In order to avoid these problems, the Prohaszka et al. patentsuggests the utilization of a cooling cone which directs an air-waterspray in a conical form about the tubing. However, this approach is notentirely satisfactory since the tubing must cool sufiiciently beforebeing subjected to such a water spray, or it could be deformed out ofround. Over cooling can result in checks and crazing. In addition, sincethe conical spray appears to merely make a circular line contact withthe tubing, the cooling application is not particularly eflicient.

SUMMARY OF THE INVENTION The present invention obviates the problemsencountered in cooling tubing by theprior art devices, and actuallyimproves cooling rates to an extent that production can be increased bymore than 60% When cooling a continuous cylindrical length of glasstubing with air, whether it be hollow or solid, the cooling rate isproportional to the diameter of the tubing, the temperature differencebetween the glass tubing and the air, and the relative velocity of theair to the tubing. Therefore, for a given size tubing being formed at apredetermined temperature and speed, I have determined that the onepractical controllable variable for cooling the tubing with air at roomtemperature is the velocity of the air. In embodying such concept, myinvention employs the utilization of high velocity air, or other gas ifdesired, within a confined region along an extended length of the hottubing as it is drawn horizontally along the supporting rollers.

In practice, a tunnel cooler of generally restricted cross sectionencloses that section of the draw which is to be cooled, including thetubing and the supporting rollers; and high velocity air is forcedthrough the restricted area between the tunnel cooler and the tubing.The most efficient method of obtaining the maximum relative velocity3,554,723 Patented Jan. 12, 1971 between the glass tubing and the gas isto create an air flow within the tunnel counter current to the directionof pull of the tubing. The exit end of the tunnel cooler is preferablyopen to the atmosphere with the inlet end closed except for a smallopening to receive the tubing, and a high capacity vacuum source isapplied adjacent the inlet end to draw air in the exit end, through thetunnel cooler, and out the hotter inlet end. An equal cooling efficiencycould be achieved by operating the tunnel at above atmospheric pressure;however, such positive pressure would cause the tubing, while still in arelatively low viscous state, to deform and become out-of-round. Thesub-atmospheric pressure, on the other hand, tends to cause the tubingto become more nearly round and provide for dimensional uniformity.

BRIEF DESCRIPTION OF THE DRAWING The figure is a schematic illustration,partially in section, of apparatus embodying my invention for carryingout the improved cooling process.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawing, glasstubing 10 is formed by a suitable downdraw process, such as from a Velloorifice 11. The tubing 10 may be pulled through a catenary 12 and alonga horizontal path 13 by means of suitable rollers 14. A plurality ofsupport rollers or diabolos 15 support the tubing 10 as it is beingpulled along the horizontal path.

A suitable cooling tunnel housing 16 of generally restricted crosssection is positioned along an extended length of the horizontal path soas to encompass both the tubing 10 and support rollers 15 along suchlength. The tunnel housing 16 is provided with a substantially closedhot inlet end 17, having a relatively small opening 18 to facilitate theinduction of the newly formed tubing 10. The opposite cooler end 19 ofthe tunnel housing is unrestricted and open to the atmosphere. Thetunnel housing 16 provides an elongated chamber or cooling zone 20 oflimited cross-sectional area adjacent the longitudinal length of tubing10. A conduit 21 is shown communicating with the chamber 20 adjacent thehotter substantially closed end 17 of the cooling tunnel housing 16. Theconduit 21 is connected to a suitable high capacity vacuum source, suchas a fan or vacuum pump 22.

In operation, newly formed hot tubing 10 enters the cooling tunnelhousing 16 through small opening 18 in the closed end 17, and exits fromthe housing through the opposite large opening 19. Pull rollers 14maintain a desired pull rate on the tubing 10, which is supported bysupport rollers 15 along its horizontal path. Vacuum pump 22 creates ahigh velocity air flow through the restricted cross section of elongatedchamber or cooling zone 20 by drawing air in through large opening 19adjacent the cool end of the draw, and discharging such air throughconduit 21 adjacent the hotter end of the draw. As shown by the -flowarrows, a counter current heat exchange is provided between the movementof the glass tubing and the air flow, so as to obtain maximum relativeair -flow velocity with respect to the glass and thereby provide optimumcooling efliciency.

While the most efficient means of cooling is to have the point ofwithdrawal of the air at the hotter end of the draw for counter-currentheat exchange, the point of withdrawal may be located at any point alongthe length of the tunnel so long as at least one of the ends of thetunnel is open to the atmosphere. The elongated tunnel provides anextended cylindrical surface contact between the glass and air, thusproviding for increased cooling efficiency. Further, as previouslypointed out, superatmospheric pressure may be utilized in place ofsubatmospheric pressure to achieve the same degree of cooling; however,I have found that uniformity of tube quality is enhanced by utilizingsub-atmospheric pressure. Additional efficiency can be achieved byblackening the inside surface of the tunnel so that more heat can beabsorbed by radiation from the glass.

As a specific example, but by no means limiting in nature, hollow tubinghaving a .45" CD. was introduced into one end of a 30 blackened coolingtunnel housing at a temperature of about 550 C. and at a rate of about10 feet per second. The tunnel housing had a cross-sectional area ofabout 40 sq. inches, and a counter current vacuum air flow of about 100ft. per second was provided through the tunnel housing by a suitablefan, resulting in the tub ing being cooled about 100 C. as it passedthrough the elongated cooling chamber provided by the tunnel housing.This represents an increase in cooling rates of more than 3 times thatobtained in an open 30' length with the usual ambient air-radiationcooling.

It can be well appreciated that various parameters may be varied toaccommodate different production operations and facilities. Forinstance, depending upon the rate of draw and diameter of the tubing,the elongated cooling chamber may vary from 5 to 40. If desired, the aircould be cooled to increase the temperature differential between theglass and air, and thus increase the cooling rate. Also, optimumefficiency of the tunnel cooler may be obtained by reducing thecross-sectional area, or increasing the length of the tunnel, orincreasing the capacity of the fan, all of which will increase thevelocity of the air with respect to the tubing, thus increasing theoverall efficiency of the cooling operaiton. Although the preferredembodiment has been shown with respect to hollow tubing, it isunderstood that the invention is equally appliciable to solid tubingsuch as cane or rod, and that various changes and modifications may bemade thereto without departing from the spirit and scope of theinvention as defined in the appended claims,

I claim:

1. An improved method of manufacturing hollow and solid glass tubing bya tube drawing process which comprises, pulling such newly formed glasstubing in one direction along a defined path at a predetermined rate,and passing a confined stream of high velocity air in an oppositedirection over the surface of such tubing along an extended length ofsuch path.

2. An improved method of forming glass tubing as defined in claim 1wherein sub-atmospheric pressure is applied to such path adjacent to thepoint where the tubing enters such path.

3. Apparatus for cooling newly formed glass tubing which comprises, anelongated cooling tunnel housing, said housing having a closed end witha small opening for the introduction of the tubing therewithin, theopposite end of said housing being open to the atmosphere, said housinghaving a cross-sectional area sufficient to encompass both the tubingbeing drawn therethrough and supporting rollers for such tubing, andmeans communicating with said housing adjacent its closed end forproducing a high velocity stream of air through said housing toward saidclosed end.

4. Apparatus as defined in claim 3 wherein said means for forming a highvelocity stream of air through said housing is a vacuum producing means.

5. Apparatus as defined in claim 3 wherein means pull said newly formedglass tubing through said cooling tunnel housing in one direction, andsaid high velocity air stream producing means provides a high velocitystream of air in an opposite direction through said cooling tunnelhousing.

6. Apparatus as defined in claim 3 wherein said cooling tunnel housingis provided with a blackened inside surface to increase the absorptionof heat from the glass tubing by radiation.

References Cited UNITED STATES PATENTS 1,766,638 6/1930 Howard 87X1,892,126 12/1932 Bailey 6587X 3,190,739 6/1965 Wilson 6586X 3,298,8081/1967 Macks 6586X FOREIGN PATENTS 1,356,644 5/1963 France 65-187 FRANKW. MIGA, Primary Examiner US. Cl. X.R.

